Perovskites based/dense membranes

In the catalytic partial oxidation of methane to produce syngas the use of permselective dense perovskite membranes avoids (or minimizes) the need of air separation, the most costly step in the process. Although both these O2- and H2-permeoselective membranes (based on perovskites or thin supported Pd-based dense films, respectively) have still to be further developed for commercial applications the outlook appears quite interesting for intensifying various large chemical processes. 

The authors found that the perovskite BCFNO membrane itself possesses a poor catalytic activity to the oxidation of CH4 in COG, which is possibly due to a lower surface area of the dense membrane. However, the conversion increased dramatically when using a catalyst bed on the permeate side of the membrane. In any case, the oxygen partial pressure in the off-gas was zero indicating that all permeated oxygen was used for the partial oxidation reaction. In particular, when the Ni-based catalyst was packed on the membrane surface, a high oxygen permeation flux of 15ml/(cm min), a CH4 conversion of 92%, and a H2... 

Unlike porous membranes, dense membranes based on perovskites or other MIEC materials offer in theory infinite selectivities to O2, H2, and CO2. Any... 

It is well known that dense ceramic membranes made of the mixture of ionic and electron conductors are permeable to oxygen at elevated temperatures. For example, perovskite-type oxides (e.g., La-Sr-Fe-Co, Sr-Fe-Co, and Ba-Sr-Co-Fe-based mixed oxide systems) are good oxygen-permeable ceramics. Figure 2.11 depicts a conceptual design of an oxygen membrane reactor equipped with an OPM. A detail of the ceramic membrane wall... 

Dense ceramic ion-conducting membranes (CICMs) are emerging as an important class of inorganic membranes based on fluorite- or perovskite-derived crystalline structures [18]. Most of the ion-conducting ceramics discovered to date exhibit a selective ionic oxygen transport at high temperatures >700°C. Ionic transport in these membranes is based on the following successive mechanisms [25] ... 

A SEM micrograph of a co-sintered multilayer reactor is presented in Fig. 6.8 no delamination or interfacial reaction can be observed on the membrane. These co-sintered multilayer reactors, only based on perovskite materials, present higher oxygen flux than dense 1 mm thick membranes in an air/argon gradient. 

The principles behind this membrane technology originate from solid-state electrochemistry. Conventional electrochemical halfceU reactions can be written for chemical processes occurring on each respective membrane surface. Since the general chemistry under discussion here is thermodynamically downhill, one might view these devices as short-circuited solid oxide fuel cells (SOFCs), although the ceramics used for oxygen transport are often quite different. SOFCs most frequently use fluorite-based solid electrolytes - often yttria stabUized zirco-nia (YSZ) and sometimes ceria. In comparison, dense ceramics for membrane applications most often possess a perovskite-related lattice. The key fundamental... 

Middelkoop, V., Chen, H., Michielsen, B., et al. (2014) Development and characterisation of dense lanthanum-based perovskite oxygen-separation capillary membranes for high-temperature applications. Journal of Membrane Science, 468, 250-258. 

Concerning non-porous membranes, these are categorized as dense ceramic electrolytes such as yttria-stabilized zirconia (YSZ) and perovskite membranes [16], which allow only the permeation of ionic oxygen. Permeation through metal membranes such as palladium and a palladium alloy is based on the selective dissolution of hydrogen and diffusion through the metal membrane. 

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